Story!
For getting the Enigmarillion you have to search it in the computer (library 2nd floor).
The book is on the Art aisle, in the space 2C, but it's not the proper Enigmarillion yet.
For converting it into the Enigmarillion, you have to organize the 8 books in the first floor so that they form an octagon.
If you organized them properly, there should be a space in the middle, put the Enigmarillion in it to transform it and win the achievement.